I chose based on what I wanted to do with the filter. I am a certified klutz, and deliberately chose the filter I didn't have to carry a kit for or service in the field. All of the filters available from major mfrs will work if they are used in areas where viruses aren't a concern.

Most filters either have ceramic or glass fiber cartridges. The ceramic ones require maintanence which scrubs away layers of the ceramic to handle the clogged pores, until you are down to nothing and need to replace the cartridge. The glass fiber filters (Hiker, Hiker Pro, and my ULA Amigo Pro) will eventually clog and require replacement of the cartridge. There is a screen around the pleats of the filter that can be removed and cleaned, but other than that there isn't much to do in the field with this filter.

All of them will remove bacteria/cysts down to .3 microns. For virus removal you will need a different brand or to add something like Micropur or Aqua Mira - viruses will be killed by chemicals within 15 minutes. Longer wait times may be necessary depending on the condition of the water, but I'm assuming you filtered it already. :)

The lightest cartridge filter I use is the ULA Amigo Pro at 8 oz, but gravity filters are not for everyone. I like that it's a dual use item (also works as a backcountry shower).

I guess I should alliterate a bit more as well as carrying my mechanical filter I carry a dropper bottle with bleach and I use it when I am using dirty of questionable water like murky lake water although I try to find a cleaner water source. As well as having the option to boil my water if my filter fails.

I have never carried any field service kit other than a small piece of scotch-brite pad for any of my gear. In my opinion if I have to do field service or repairs on any of my gear I don't need that piece of gear. All of my gear gets cleaned and maintained as needed when I get home from my trip.

First Need XL FTW. Not the lightest, not the smallest, but it kills everything, is very rugged, is field servicable/backwashable (but you should never have this issue), and improves the taste of the water. It will even remove most, if not all, of fecal coliform collonies in your water, depending on the location. If your travels might take you overseas, or to any 3rd-world countries, the First Need XL is THE filter/purifier to have. You won't have to mess with any drops or tablets in addition to your filter, which means no additional wait time to drink your water. I've sucked up the brownest, most stagnent water through the First Need--the stuff in puddles where you have to sweep aside the oily film--and get only the clearest, cleanest drinking water out the other end. Every time. It also has the capability to mate with virtually any size bottle opening out there, from nalgenes to patys to pop bottles.

Advantages: Sweet Water pumps on both up and down strokes. Remove the handle to make it easier to use and lighter.

Hiker Pro: Compact and lightweight. A reliable favorite among AT Thru-hikers

Mini Works: Can be cleaned easily on the trail. Just remove the ceramic filter and clean it with a piece of a dish cleaning pad. Sandy water in a canyon puddle can be filtered clean, because the filter can be so easily cleaned of filtered sand that would soon clog other filters.

Hyper flow: Works well in clean water only. Clogs fast, but reverse flow cleansing can be done in the field. It pumps water fast, but because of easy clogging, I would not recommend it.

Easiest and lightest (other than AquMira) is the Streri Pen. Other options are the gravity filters (ULA-Equipment). Fill a water bag. Hang the bag and gravity pulls the water through a filter, down a tube into your bottle. This works best when the bag is full. The process works, but takes a bit more time. For other makes of gravity filters, a long hose is needed. The ULA Gravity filter works well. They use the same filter used in the Hiker Pro.

Aquamira is the easiest, but I do not like using chemicals for long periods of time. No scientific reason. The Steri Pen is convenient, too, and for short trips the battery will last. (It is a CR type) I put water for treatment into the pot I use for cooking, then pour the treated water into a platypus bottle. I use a small funnel that attaches to the platypus, covered with a piece of no-seeum netting to filter out "floaties". The funnel comes from Hennessy Hammocks and is used as a line tensioner system for hammocks. At their website, scroll down at accessories. (NB Hennessy does not end in s-e-y, no "e" !)

Re-Read comments by "Not quite there"!

PS The Mini works fits right on top of a Nalgene bottle. All can be rigged to attach to the top of platypus and nalgene containers, so you can pump directly into the containers.

As you can see from the above comments, they all work. It comes down to personal preference. Except for the Vario, I have used all of the mentioned filters and have never been sick from drinking water even in the Peace Corps where we used carbon gravity filters and kept boiled water in ceramic jugs.

Hi,
I been hiking for weeks at a time and never used a filter but I know I should and I'm planning on getting one.
I am planning a year trip via Asia and going to do about half the way by foot so which and ever lasting are the key...
I am thinking about the MSR MIOX - I can't see myself filtering all the water I'm going to use, will do it only when I think I should and the Miox is only 100gr...
Someone used it over here?

I've used a First Need, a Timberline, and the Hiker. Of the three, the Hiker is the one I've stuck with for many years now. I find it works better for me in more conditions than the others. Since it is so popular, parts and replacement filters are easy to find. There are other great filters out there, and someone to swear by any of them, but I'm happy with the Hiker. Spend a little more money and get the Pro, though; it has some handy improvements that make it easier to use, like quick-attach hoses.

Sweetwater works great and is fairly compact. Replacement cartridges are available for affordable price. We've used the same pump for about 5 years now and changed the cartridge just 3 times. I figure we've filtered about 40 gallons of water with it.

I'm with pillowthread. I like the First Need XL the best and use chlorine dioxide tablets as an emergency backup. I've tried every other system on the market and myog variations and I still think it's the best, most cmplete, most reliable purification or filter system out there - that is light enough to carry in a backpack. I'll add that my base gear weight is 10-12 lbs.